Re: [sr-dev] Why fetch docbook stylesheets remotely?

On Fri, Oct 16, 2009 at 5:18 PM, Jan Janak &lt;jan(a)ryngle.com&gt; wrote: After second reading of emails in this thread I realized that my earlier explanation of the Docbook system is not only confusing, but also incorrect. I apologize, please forget what I wrote in the email sent yesterday and let me try again. The usual text at the beginning of Docbook source documents <!DOCTYPE section PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN" "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd"> determines the particular version of the DTD (Document Type Definition) the Docbook document tries stay compatible with. This information is only used if you try to validate your Docbook document against the schema, for example by running make check in sip-router or if you use an editor which performs document validation on the fly as you edit the document. The HTTP URL in the example above refers to the DTD file online, this is the recommended way of writing DTD declarations in Docbook XML files. If you actually try to download the document then you get the DTD file for Docbook version 4.2. If you try to validate a Docbook document in sip-router by typing "make check" in a doc directory then the makefile system runs xmllint to validate the document. Xmllint uses the document type declaration presented above to locate the DTD file needed for the validation. But before it tries to download it using the HTTP URL above, the tool consults the file sip-router/docbook/catalog.xml to see if there is perhaps a local copy of the file already on a local disk. The file catalog.xml is a XML catalog file. XML catalog files are used to map document type declarations (like the one above) to local files. XML catalogs can map both type of identifiers, the textual one "//OASIS//DTD.." and the HTTP URL as well. If the catalog file has a reference to a local DTD file then Xmllint uses the local file and does not try to download it from the HTTP URL. If there is no local copy of the DTD file then Xmllint downloads it using the HTTP URL above. The XML catalog file in sip-router/docbook/catalog.xml refers to system-wide "standard" catalog files by default. On Debian (and perhaps other Linux/GNU based systems) the system-wide catalog is /etc/xml/catalog. On Debian systems the system-wide catalog file is updated by the package manager. That means if you install the package docbook-xml, which contains Docbook DTD files for all 4.x versions, the DTD files from that package become automatically available to the Docbook build system in sip-router and it never has to download anything from the internet.